This invention relates to a structure useful as a guidewire for medical purposes. More particularly, the invention relates to a structure with anti-creep properties and suitable softness, and preferably substantial torque control, usable as a guidewire in connection with medical treatments.
Guidewires are often utilized in placing catheters and other implements into the bodies, e.g., blood vessels, various cavities and the like, of medical patients. Such guidewires may have to be manipulated through long and tortuous paths. They must have sufficient column strength to be able to direct the implement to be placed in the patient's body while,. at the same time, being flexible enough to negotiate the often tortuous path and being soft enough to avoid unduly damaging or injuring the path.
One problem which has plagued guidewire constructions, especially all plastic guidewire constructions, is the phenomenon called "creep". This is defined as the susceptibility of a material, e.g., a plastic material, to become deformed by the application of a low level force over a long period of time. An example of this creep property is the "set" that plastic tubing often assumes after being coiled in a box. Upon removal from the box, the length of tubing will maintain its coiled configuration to some extent. It is desirable, e.g., in order that the guidewire have good ability to be deformed as desired to pass through the body, that the guidewire has a reduced tendency to creep or an enhanced anti-creep property.
The term "torque control" as used herein refers to the ability of a guidewire to transmit twisting forces along its length, and satisfactory guidewire performance often depends on this ability. Satisfactory torque control enables carefully controlled maneuvering of the guidewire within the patient's body by skilled manipulations at the guidewire's proximal end. Thus, torque control is important and increases in torque control are advantageous.
A number of guidewire constructions have previously been suggested. For example, Herlitze U.S. Pat. No. 4,504,268 discloses a stiffening rod for a catheter comprising at least one resilient, high tensile strength multifilament strand, made of non-rusting steel, embedded in a plastic rod having a high percentage of x-ray contrast material to make it easier to detect the catheter by x-ray. Herlitze teaches that the high tensile strength filaments, which are placed in the center of the stiffener without being bound together, impart high tensile strength to the rod and reduce the probability of the rod breaking. However, since the filaments are separate and not a unitary structure, torque control of the Herlitze stiffener may not be acceptable. Also, since the filaments are not bound together, hollow areas and inconsistencies in strength, i.e., weak spots, along the length of the stiffener may be troublesome. Herlitze is concerned with x-ray detection of the catheter and not with the anti-creep properties or torque control of the stiffener.
Yoshimura, et al U.S. Pat. No. 4,345,602 discloses a vascular guidewire which has a varied structure, i.e., a varied cross-section, along its length. This device includes a tip part, a flexible part, a tapering part and a manipulating part, with each part having its own structural characteristics. An x-ray impermeable material, such as a tungsten wire, is inserted into the hollow of the manipulating part for imparting proper toughness and rigidity to this part. The relatively complex, variable structure of the Yoshimura et al, guidewire is relatively difficult and expensive to manufacture. Further, Yoshimura, et al is not concerned with the anti-creep properties of the guidewire.
Beal U.S. Pat. No. 4,257,421 discloses a flexible rod formed by applying water soluble USP gelatin to a multi-strand nylon thread base in a spiral twist. The water soluble coating allows the rod to be removed from the tube, which it is used to place in a patient's body, by dissolving the gelatin. The gelatin coating, in its undissolved state is less flexible than the nylon thread base. Beal focuses on ease of removing the rod after use rather than on anti-creep and torque control properties.
There continues to be a need for a guidewire construction which has enhanced anti-creep properties, and preferably increased torque control.